"The Disarming Charm lies at the heart of a good dueling technique. It allows the duelist to rebound an opponent's spell in the hope that the rebounded spell will strike the opponent and leave him or her vulnerable to further attack."

The Disarming Charm,[1] also known as the Expelliarmus Spell[4] or Disarming Spell[5] (Expelliarmus) was a defensive charm which forced the victim to release whatever they were holding at the time. It is common to see this spell used in duels, to make an opponent release their wand.[1]

Effects

Harry casting a powerful disarming charm indicated by the scarlet jet of light

The Disarming Charm causes whatever an opponent is holding at the time — usually a wand — to fly high out of their reach.

The Disarming Charm always appears as a jet of red light; indeed, this is one of the things that makes it recognisable before the effects of the charm are seen. However the intensity of the light appears to correspond to the strength of the spell as a weak/moderate one creates a small flash of white light whereas a more powerful version manifests as a bright jet of scarlet light. Another noteable effect of the charm is that if multiple charms are used on the same target, the target will be disarmed, but at the same time will be blasted backwards, as seen when Harry, Ron and Hermione all used the Disarming Spell at once on Severus Snape in the Shrieking Shack.

Priori Incantatem

If two wands with the same core are forced to do battle with each other, the effect is a magical connection called Priori Incantatem. When Priori Incantatem occurred between Lord Voldemort and Harry Potter, the latter was using the Disarming Charm, a much weaker spell than the former.

Known uses and practitioners

"They made the most of the last few hours in which they were allowed to do magic before the holidays... and practised disarming each other by magic. Harry was getting very good at it."

In the films only when a witch or wizard is locked in the Priori Incantatem is the spell scarlet. When not locked in combat it's always just a blue or white flash that will either connect with the target's hand and force the wand out of their hand or will blast them off their feet, sometimes unconcious.

When Dumbledore used this on Snape, it appeared as white lightning, and hence was probably a variation of it rather than the spell itself, or else an entirely different disarming spell.

In the second film, it appears as a golden ring; from the fifth film onward it was a ball of blue light.

In the video games, mainly he console versions of the first and second games, the Disarming Charm worked rather like a Shield Charm, rebounding an opponent's spells upon them. This is actually also the describing of the spell in the The Standard Book of Spells series. This was mainly due to the lack of being able to disarm in past video games.

Also in the console version of the second game, it's possible to catch and deflect spells not only cast by prefects in the PS2 version, but it's also possible to do so on one's own backfired spell. This only works on Flipendo and Incendio however, as the other projectile spells will pass through. In the case of the former, it moves rather fast so tight timing to activate the charm is needed.

The Disarming Charm is referenced on Doctor Who, when Shakespeare uses it to conclude a formula used to banish the villains from earth. The Doctor (played by David Tennant) smiles after the villains are beaten and says: "Good old J.K.", referencing the author of the Harry Potter series.